1. Field of the Invention
The present invention relates to a display device, more particularly to a color adjustment device, a method for adjusting color and a display for the same.
2. Description of the Prior Art
Based on a conventional image processing technology, a display area on a LCD panel is divided into multiple pixels, each of which comprises sub-pixels of displaying red, green and blue. Because all colors of visible light can be made by mixture of red, green and blue light, a required color shown in a pixel can be constructed by controlling luminance value of the red, green and blue sub-pixels.
To describe color more appropriately, the International Commission on Illumination, hereinafter referred to as the CIE, proposed the CIE 1931 XYZ color space, in which regard red, green and blue as three primary colors, and all other colors can be generated by mixture of the three primary colors. Two light sources, made up of different mixtures of various wavelengths, may appear to be the same color; this effect is called metamerism. Two light sources have the same apparent color to an observer when they have the same tristimulus values, no matter what spectral distributions of light were used to produce them. In this case, the two light sources have the same tristimulus values X, Y and Z which refer to proportions of the three primary colors. The CIE 1931 XYZ Space usually shows as the CIE 1931 chromaticity diagram, of which three parameters Y, x, y, where Y refers to luminance value, that is the stimulus value Y, while x and y refer to chromaticity values. In this case, x=X/(X+Y+Z), y=Y/(X+Y+Z), z=Z/(X+Y+Z). Because x+y+z=1, z can be expressed in x and y.
When LCD panels display, color derivation probably occurs even if they are showing the white color at the same grayscale. In order to attain accuracy and consistency of colors on the LCD, it is necessary to perform white balance for each LCD. The method of white balance is as followed: At first, make pixels of the LCD show as white at all grayscales, and then adjust gain values of the strength of red, green and blue so that the chromatic values and the luminance value of the white performed on the LCD approaches a set of chromatic values and luminance value of a target white, that is, the white performed on the LCD is adjusted within a certain range of color temperature and color derivation.
Referring to FIG. 1, FIG. 1 shows a graph of relation between white and chromatic value in grayscale 0 to 255, according to the CIE 1931 XYZ color space, where Wxn and Wyn refer to the chromatic value x, y required to perform as white when grayscale n (n=0, 1, 2, 3 . . . 254, 255). FIG. 1 shows that the chromatic values x, y of various white at different grayscale in the CIE 1931 color space. For instance, at the grayscale 50, when Wx50=0.285 and Wy50=0.295, the pixel performs as white. In other words, by adjusting the grayscale applied to the RGB sub-pixels of the pixel so as to the chromatic value of RGB sub-pixels meet Wx50=0.285 and Wy50=0.295, the pixel is performing as white. Take FIG. 1 for example, at higher grayscales, e.g. grayscale 40 to 255, the ratio of the chromatic values x and y is a constant, that is, Wx255=Wxn=0.285 and Wy255=Wy50=0.295, n=40, 41, . . . , 255, while at lower grayscales, e.g. grayscale 1 to 40, the ratios of the chromatic values x and y are diverse.
In the dark state, the chromatic value performed on the panel usually drifts to blue. If it still remains the colorimetric as that of the grayscale 255, it is inevitable to increase proportions of red and green. As a result, the luminance increases while the contrast on the panel decreases at the dark state. Simultaneously, for human's sight, the variation of luminance brings in the chromatic variation. For human's sight, bluish dark state seems more real than the dark state in unchanged chroma does. Therefore, traditionally, the chromatic coordinate of the grayscale 0 is (x0, y0) and the chromatic coordinate of the high grayscale, such as the grayscales greater than 32 in FIG. 1, is (x255, y255). The colorimetric coordinates of the grayscale 1-32 can be obtained by linear method:
            x      n        =                  x        0            +                        (                                    x              255                        -                          x              0                                )                ·                  n          A                      ,          ⁢            y      n        =                  y        0            +                        (                                    y              255                        -                          y              0                                )                ·                  n          A                      ,          ⁢      (          n      ∈              [                  1          ,          A                ]              )  Where (xn, yn) is the chromatic coordinate of the grayscale n, A=32.
At the grayscale 32, however, discontinuity occurs in the chromatic variation, which causes chromatic inconsistency for human's sight. As a consequence, it becomes an object of the industry to develop a color adjustment device, a method for adjusting color and a display for the same, with a more decent colorimetric curve for human's sight, causing the grayscale variation seems more natural for human's eyes in the process of white balance.